Learn Hardcore Italian: Il libro diventa interessante.

In Italian, il is the standard definite article used for singular masculine nouns that begin with a consonant. Since libro is masculine and starts with a consonant, we choose il.

What tense and person is diventa?

Diventa is the third-person singular present tense form of the verb diventare. It agrees with il libro (which is singular), indicating that the book is in the process of becoming something.

Why do we use interessante and not interessanti?

In Italian, adjectives must agree in number and gender with the noun they describe. Since libro is singular and masculine, the singular masculine form of the adjective is interessante (which also happens to be the same for feminine singular in this particular case). If libro were plural (e.g., i libri), we would use interessanti.

What is the difference between diventa interessante and è interessante?

Using diventa interessante (from the verb diventare) focuses on the process of the book transforming from not very interesting to interesting. On the other hand, è interessante (from the verb essere) simply states that the book is interesting as a current fact without emphasizing any change over time.